Numerous devices have been described for use in spraying various substrates from simple spray cans to robotically controlled articulating mechanisms. In the roofing industry, flat or low pitch roofs are often coated with one or more layers of coating such as polyurethane, silicone, or acrylic resin in order to provide insulating, UV, or waterproof barrier. Although many different types of spray applicators are available, with the known devices it is difficult to maintain uniform film thickness especially when applying a composition which expands or foams during application.
U.S. Pat. No. 3,379,377 relates to a spraying apparatus for automatically applying a coating of fluent material to an article of manufacture wherein a trolley mounted on an elevated support rail carries a sprayhead which is operable to spray an underlying article of manufacture during reciprocal movement of the trolley and it sprayhead along the support rail.
U.S. Pat. No. 3,383,046 relates to an apparatus for spraying a coating on a substrate, and more particularly to apparatus for spraying a coating of controlled irregular thickness.
U.S. Pat. No. 3,954,544 relates to an apparatus for in situ preparing and applying foam to a surface, such as a roof, and at the same time applying a membrane onto the surface of the foam, produces a foam-membrane sandwich held to the treated surface.
U.S. Pat. No. 5,670,178 relates to foamed plastic applied on a roof substrate by progressively dispensing expandable plastic foam material on the substrate along a path and progressively confining the vertical and lateral expansion of the material along the path and relative to the substrate. Apparatus for applying the foamed plastic comprises a platform having opposite ends and opposite sides having an endless belt supported on the platform for displacement relative thereto in the direction between the opposite ends. The belt is supported above the roof substrate by laterally spaced rails or by tracks on the belt, and a motor is provided on the platform for driving the belt to move the platform along the path. A dispensing gun is supported on the front end of the platform for dispensing expandable plastic foam material onto the substrate ahead of the belt and vertical and lateral expansion of the material is reportedly confined by the belt and rails or tracks as the platform moves along the path.
U.S. Pat. No. 6,036,123 relates to an apparatus for applying foamed plastic material on a roof deck which comprises a wheeled frame moveable along the deck and carrying a foamed plastic dispenser support and drive assembly which extends transverse to the direction of movement of the frame and which includes a carriage reciprocal in opposite directions along a linear carriage path and supporting a foamed plastic dispenser for reciprocation therewith and for pivotal displacement relative thereto at each of the opposite ends of the carriage path about a horizontal axis transverse to the carriage path so as to pivot the dispenser for discharging the foamed plastic material laterally outwardly of the ends of the support and drive assembly.
U.S. Pat. No. 6,358,344 relates to a method and an industrial robotic device for uniformly applying coatings upon a surface moves a spray applicator foam dispenser between two parallel tracks. The application of foam at each pass is performed by accelerating the speed of the foam dispenser at the end of each pass, by providing respective curved uphill distal ends of the tracks, so that the spray applicator foam dispenser moves up the curved distal ends and returns quickly while changing speed, tilt, and direction at the end of each pass.
The prior art devices suffer from numerous drawbacks. Prior art devices having limit switches at distal ends of a rail with a carriage moving therebetween often provide coatings which are relatively thicker at each end than in the middle due to the dwelling of the carriage at the end points during direction reversal. Spraying devices having an arced rail often are prone to overspray and/or flared out material at the ends of the spray path. Accordingly, some prior art devices are not suitable to allow for close proximity spray applications wherein the flare of a coating material would be cast on to an object that is not intended to be covered by the coating.